Alignment films are formed on portions connected directly to liquid crystal molecules in liquid crystal display devices, and as a functional thin film controlling the alignment of liquid crystal molecules, materials for alignment films have a very important role in determining the display characteristics of liquid crystal display devices.
Currently, a variety of polymer compounds have been known as compounds used for liquid crystal alignment materials. Of them, the mostly-used representative compounds are polyimide based polymer compositions which use polyamic acids through imidization. Also, according to the documents that have been known so far, a variety of polymer compositions such as polyacryis, polyvinyls, and polyamides substituting the hydrogen atom of amide bond with other monovalent organic group have been proposed. However, as they involve insufficient problems in alignment properties of liquid crystal molecules, electrical-optical characteristics, coating performance, heat resistance, drug resistance, etc., very few cases have been put to practical use.
Polyimide has been used as insulating materials, protection materials, etc. in electric and electronic material fields due to its inherent high mechanical intensity, heat resistance and solvent resistance and it has also been spotlighted as materials for liquid crystal alignment films of current liquid crystal display devices because films can be easily formed uniformly and it has excellent durability. Recently, however, as technologies about liquid crystal display devices are developing, new characteristics that did not exist for materials for liquid crystal alignment films before are required.
Basic requisites for liquid crystal alignment films are the control of pretilt angles. It has been known that the pretilt angles of liquid crystal molecules are greatly affected by the shape of the surface of alignment films and the length of side chains. In particular, liquid crystal display devices of VA mode require high pretilt angles of 88-90 degree. Generally, as means for obtaining high pretilt angles, there have been used side-chained polyimide compounds. However, it is difficult to obtain alignment having uniformly high pretilt angles throughout the whole regions of broad substrates by the mere use of side-chained polyimide compounds. To obtain such high pretilt angles, there have been developed polyimide liquid crystal alignment materials using as a monomer, an aliphatic side-chained diamine having a straight alkoxy group or un-saturated alkyl group as a side chain, but as the distribution and length of the side chains are not controlled in such polyimide alignment films, their pretilt angles were often as low as 3˜25 degree or so.
For example, Japanese Patent Laid-Open No. 5-043687 describes liquid crystal display devices using liquid crystal alignment films using polyimide resins having as a repeat unit, a compound represented by the following structure 1:

wherein A is a tetravalent organic group constituting tetracarboxylic acid and its derivatives, B is a bivalent organic group constituting diamine, and n is an integer.
However, it was difficult to obtain pretilt angles around 90 degree by using the above polyimide alignment film, and after-image frequently occurred. Furthermore, the mixtures of polyimides and polyamic acids were separated by heat, and liquid crystal alignment materials prepared by the block copolymerization of the polyimides and polyamic acids involved too complicated preparation routes.
Also, Korean Patent Laid-Open No. 2004-0069565 discloses diaminobenzene derivatives having a long-chained alkyl group or alkylcyclohexylphenyl group as a side chain and polyimide liquid crystal alignment films using the same.